Abstract

Objective

To develop a thermochromic tissue-mimicking phantom (TTMP) with an embedded 3D-printed bone mimic of the lumbar spine to evaluate MRgFUS ablation of the facet joint and medial branch nerve.

Materials and methods

Multiple 3D-printed materials were selected and characterized by measurements of speed of sound and linear acoustic attenuation coefficient using a through-transmission technique. A 3D model of the lumbar spine was segmented from a de-identified CT scan, and 3D printed. The 3D-printed spine was embedded within a TTMP with thermochromic ink color change setpoint at 60 °C. Multiple high energy sonications were targeted to the facet joints and medial branch nerve anatomical location using an ExAblate MRgFUS system connected to a 3T MR scanner. The phantom was dissected to assess sonication targets and the surrounding structures for color change as compared to the expected region of ablation on MR-thermometry.

Results

The measured sound attenuation coefficient and speed of sound of gypsum was 240 Np/m-MHz and 2471 m/s, which is the closest to published values for cortical bone. Following sonication, dissection of the TTMP revealed good concordance between the regions of color change within the phantom and expected areas of ablation on MR-thermometry. No heat deposition was observed in critical areas, including the spinal canal and nerve roots from either color change or MRI.

Conclusion

Ablated regions in the TTMP correlated well with expected ablations based on MR-thermometry. These findings demonstrate the utility of an anatomic spine phantom in evaluating MRgFUS sonication for facet joint and medial branch nerve ablations.

中文翻译：

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腰椎的解剖学热变色组织模拟体模，用于对小关节的MR引导聚焦超声（MRgFUS）消融进行临床前评估

摘要

目的

用嵌入式3D打印的腰椎骨模拟物开发热致变色组织模拟体模（TTMP），以评估小关节和内侧分支神经的MRgFUS消融。

材料和方法

选择了多种3D打印材料，并使用直通传输技术通过测量声速和线性声衰减系数来进行表征。从身份不明的CT扫描中分割出腰椎的3D模型，并进行3D打印。将3D打印的书脊嵌入TTMP中，并在60°C下使用热致变色墨水颜色更改设定点。使用连接到3T MR扫描仪的ExAblate MRgFUS系统，将多个高能超声定位到小关节和内侧分支神经的解剖位置。与MR测温仪上预期的消融区域相比，解剖体模以评估超声处理目标和周围结构的颜色变化。

结果

测得的石膏的声音衰减系数和声音速度分别为240 Np / m-MHz和2471 m / s，这与已发表的皮质骨最接近。超声处理后，对TTMP的解剖显示，幻影内的颜色变化区域与MR测温仪上预期的消融区域之间具有良好的一致性。在关键区域没有观察到热沉积，包括颜色变化或MRI产生的脊管和神经根。

结论

TTMP中的烧蚀区域与基于MR测温法的预期消融密切相关。这些发现证明了解剖脊柱体模在评估MRgFUS超声对小关节和内侧分支神经消融方面的实用性。